How to Calculate and Generate a Cpk Chart

[Charlie Tee]

Hi,

Any expert can help me out?
I just generate x bar - r chart in excel
I wish can add in the cpk chart into this worksheet...
I need somebody help...no idea at all...

I attached my x bar - r chart.xlx someone can help me to modified to add on cpk or not?

 

[Barbara B]

Re: How to Calculation and Generate a Cpk Chart

I wish can add in the cpk chart into this worksheet...

For the Cpk calculation you have to provide tolerance limits (at least 1), but I don't understand your idea of adding a Cpk into the chart, as the values of the Cpk lie (presumably) outside your parameter range (3.80,4.20)

 

[Darius]

Another way to understand Chart is a report with Charts (not a specific Chart), so Charlie want to put Cpk on the report but don't know how to calculate.

Charlie, in your report, I can't see your specification limits, without them is not possible to calculate.

Cpk = min (X_Average-LSL, USL-X_Average)/(3Sigma)

As you didn't ask for Cp, looks like your process may have only one spec limit, so use the only one if it is the case.

Extracted from your formulae

3Sigma = 0.58*R_Average.

 

[Charlie Tee]

Dear,

The limit spec only have "Minimum Spec", means >3.8 kgf is acceptable...
The CPK　ｉｓ　ｒｅｑｕｉｒｅｄ　ｂｙ　ｍｙ　Ｍａｎａｇｅｒ．　Ｉ　ａｌｓｏ　don't know what purpose he want the cpk chart...T.T

Thanks,
Charlie

 

[bobdoering]

I added a Cpk chart based on the calculated standard deviation of each sample set of data. It uses only one specification, and really is a horrible statistic. Cpk is designed to determine if your mean is in the middle of a specification. By using only a unilateral specification, you are kind of just reporting a distance from the specification. It does not directly relate to the original concept of centering your mean within the specification. It appears to be a rubber stamp of Cpk with no real justification of its use.

The CPK　ｉｓ　ｒｅｑｕｉｒｅｄ　ｂｙ　ｍｙ　Ｍａｎａｇｅｒ．　Ｉ　ａｌｓｏ　don't know what purpose he want the cpk chart

Neither do I - so don't feel bad!